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Talk about engine building here. New products, tricky questions or showcase your work - If it's engine building related it's welcome here.
my r35 built engine burns oil every 1500km low oil level shows in the dash and the dipstick looks low and black got it to the mechanic shop and rebuild it again with same issues no smoke while driving unless i shut it and restart it again in cold day it start smoke white for few seconds and this rarely happen then it back to normal with no smoke even in WOT
can anyone guess whats the problem?
White 'smoke' when cold isn't unusual - when fuel is burned it produces carbon dioxide and water - the latter is as steam which can condense as a white appearing vapour in the colder air. Some condensation also occurs in the exhaust system, and this is sometimes seen as a drip from the tail-pipe when it's cold.
"Oil burning" can be caused by many things, just how much oil is it actually using, and how is the vehicle being used? Are there any signs of external engine leakage?
The primary reasons for oil burning are...
Valve stem seals - these may have been incorrectly fitted, they may be the wrong type, if new valve guides were installed they may be slightly too high in the head and have been damaged by the valve retainers/caps, or if an aftermarket camshaft has been fitted it may have enough additional lift to hit the seals, or aftermarket spring kit's may not have th3e required clearance.
Oil control rings not being able to scrape the oil from the bores, this can be more of a problem with modern low-tension rings (to reduce drag and improve fuel consumption) and/or oil squirters which have higher than OEM capacity (some have restrictors that 'tuners' remove, or drill out) or have had check valves removed/stuck. This is, of course, much more of a problem if the blowby gases and/or piston temperatures cause the oil to oxidise and gum up in the ring grooves.
If it's a valve seal problem, you may see the deposits on the spark plug are mostly on one side of the central electrode, but if the deposits are roughly equal all around the central electrode, that suggests a ring problem.
There are at least a couple of other potential areas of concern - modern engines use a positive crank case breathing system, where engine vacuum under light running draws fumes from the crankcase and if there's a lot of blowby there may be excessive oil being carried into the inlet manifold with the higher amount of air being carried into the manifold. This may also colour one side of the valves, but all more evenly, rather than just a few.
Most overhead cam engines use pressurised squirters to lubricate the valve train, especially the cam lobes and followers, and they commonly use a restrictor, or check valve, to control the amount of oil passing into the top of the engine. Some 'tuners' remove these restrictors, if used, and the result is the head(s) can have more oil in them than the returns can handle properly and, in some circumstances, the oil level in the head's outer edges can be high enough to overwhelm the seals.
Your engine builder should have been able to examine the components on strip-down to see where oil deposits, stains, etc indicated where the problem(s) lay.
tottaly agree with gord